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The main source material I've used as a guide for cotter pin related matters is Barnetts, which sticks hard to its recommendation to fully degrease cotter pin taper surfaces and their spindle mating surface, and press them in dry. They recommend to grease the nut threads as one normally would with most fasteners on a bike.

When one has to rework the flat on a pin freehand, as is often the case, some amount of imprecision is introduced. Intuitively it would seem like adding lubrication would help with maximizing contact area between the surfaces despite it; i.e. it would decrease the force needed to smoosh it all into place and allow it to get into final, fully smooshed condition with less of a break-in period, which is what you want.

Is Barnetts' recommendation reflective of how most shops actually approached this during the age where cottered cranks were more prevalent, or in parts of the world where they're still encountered regularly?

What are the pros and cons of doing it either way in actual practice?

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    The first bike I ever owned had cottered cranks. That was over fifty years ago and I don't believe I greased them (much less the threads on them), but being <10 yo at the time, I was just beginning to learn. I don't recall them being too difficult to remove. Good question, and nostalgic for me as well.
    – Ted Hohl
    Commented Jun 27, 2022 at 13:21
  • Is there any distinction made between new and old/reused cotter pins? Do they work-harden over time? But Cotter pins would be under tension not compression?
    – Criggie ♦
    Commented Jun 27, 2022 at 21:08
  • I think generally speaking they're fine to reuse when both are still in good condition, both the taper and the threaded stud. A pretty high percent of the time when one is dealing with them in the first place though, that won't be true. And they generally must be replaced in pairs so the angular relationship of the cranks stays at 180 degrees.
    – Nathan Knutson
    Commented Jun 27, 2022 at 22:57
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    Nathan, my experience is that they are quite a soft material and that may be why no Lube is recommended. I have a fair few vintage maintenance books at the shop, if i have time tomorrow i’ll see what various authors in various decades had to say on the matter.
    – Noise
    Commented Jun 28, 2022 at 18:58

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I've come across a lot of oxidized cotter pins that are a right pain to remove!

For me, the biggest tip would be to use an appropriate anti-seize compound and apply it. The benefits are similar to adding it to the bottom bracket axle and crank interface on square taper cranks. You're less likely to develop play between the interfaces as you use it and it makes it easier to remove when you need to.

The only con I can think of is maybe if you use the wrong type of compound it could make the interface not connect correctly? The mechanism works by friction so it's possible a compound could make mess with this? I dunno.

I would use some light anti-seize for sure.

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    Perhaps using the crank and square taper analogy isn't beneficial here :) On most forums people will come up and tell you to put them on dry, or to use some special compound or such. I personally like my square taper interfaces greased, then torqued to spec. It is my understanding that the cotter pin is pressed in tightly, but that the friction is maintained because of the locking nut, which should resolve uncertainties arising from possible deviations in friction due to some applied compound (versus a dry, clean cotter pin).
    – jayded-bee
    Commented Jun 27, 2022 at 15:14

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